The present invention relates to an elastic-base grinding wheel for smoothing and polishing toroidal contours of hard materials.
In the art of working of hard materials, and in particular of marble finishing and polishing, grinding wheels are used to operate on the previously worked part.
The known grinding wheels are generally made of magnesite, resinous materials or the like, and in any case, they are made of rigid materials and, as a consequence, serious problems are encountered owing to variations of the thickness of marble slabs, granite or stone to be machined because since the grinding wheels known in the art are rigid, they cannot correctly match and adhere and consequently operate on the whole surface of the various contours encountered. Also, grinding wheels made out of a vulcanized rubber body are known, provided with cemented diamond-coated cloth suitable for smoothing and polishing, but this kind of construction shows both the problem of an excessive cost of the vulcanized rubber body and the problem of having a non uniform compliance since the areas where the rubber thickness is smaller, owing to their excessive flexibility, do not adhere adequately to the contour to be machined.
In practice, in grinding operation and subsequent finishing operations up to polishing or honing of rigid and hard materials such as glass, marble, granite and the like, two kinds of techniques have been developed.
The first kind entails the use of very rigid shaped bodies for grinding, finishing and polishing. The machining bodies having high rigidity are mainly utilized in extreme precision operations such as optical pieces or high-precision mechanical parts. The working operations with rigid bodies, even if they provide excellent results insofar as the dimensional tolerances are concerned, are however very slow: the optical polishing for e.g. large dimensions telescope mirrors may last for months or even years.
The second kind entails the use of either flexible or deformable shaping bodies made of felt, rubber or the like. The flexible bodies do not allow a precise working, but however allow to perform the working in extremely short times. These short working times are bound to the skill of the operator and show difficulties in working shaped bodies such as those having a toroidal contour.
As a matter of fact in working a hard material that can be polished, abrasives having a decreasing grain size are used with the progress of the finishing operations. When grinding and polishing bodies are used, which incorporate the abrasive materials, if the shaping bodies are either flexible or elastic, it is difficult to obtain a correct matching in the subsequent passes with grinding bodies including abrasives having a decreasing grain size.
EP-A-0 281 050 discloses an abrasive grinding wheel for working stone materials comprising a supporting body associable with a rotating operating assembly. According to the invention the grinding wheel comprises an elastically resilient mass peripherally defining a region with a shape substantially complementary to the shape of the part being machined. Portion in abrasive material are provided on said region.